## Parallel designs (total variance) [Power / Sample Size]

❝ I have data from a parallel pilot study and am using that to estimate the sample size for a pivotal study. The formula that I am using requires an estimate of the inter subject variability which I don't have. I have the total variability (sqrt(MSE)). Is there a way to estimate intersubject variability from a parallel design or would it be correct to use the total variability instead?

Hhm, yes you have the total variability (

*inter*- +

*intra*-subjects); the same will be true for your pivotal study. I don’t get your point of trying to estimate inter-subject variability from total. Which formula are you referring to?

❝ Would it be correct to estimate inter-subject var as sd/mean for test and reference separately and then take the average?

❝

❝ And one last question, how correct is it to take 60% of inter subject (calculated as sd/mean) to be the intrasubject variability?

I don’t think so (both questions).

For an example please have a look at

Chow SC, Wang H.

*On Sample Size Calculation in Bioequivalence Trials.*J Pharmacokin Pharmacodyn. 2001;28(2):155-69.

and

*Errata*given at

J Pharmacokin Pharmacodyn. 2002;29(1):101-2.

You will also need two letters to the editor:

Hauschke D.

*A Note on Sample Size Calculation in Bioequivalence Trials.*J Pharmacokin Pharmacodyn. 2002;29(1):89-94.

Blood P.

*Sample Size Calculation in Bioeqivalence Trials.*J Pharmacokin Pharmacodyn. 2002;29(1):95-7.

H Wang H, SC Chow SC.

*Authors’ Response.*J Pharmacokin Pharmacodyn. 2002;29(1):99.

*Dif-tor heh smusma*🖖🏼 Довге життя Україна!

_{}

Helmut Schütz

The quality of responses received is directly proportional to the quality of the question asked. 🚮

Science Quotes

### Complete thread:

- Sample size estimation for parallel design Nav Coelho 2007-07-20 16:14 [Power / Sample Size]
- Parallel designs (total variance)Helmut 2007-07-20 16:29
- Parallel designs (total variance) Nav Coelho 2007-07-20 18:38
- CV-intra # 60% CV-inter Helmut 2007-07-22 01:17
- total (pooled) variance: examples Helmut 2007-07-23 17:44
- total (pooled) variance: examples Nav Coelho 2007-07-23 19:58
- total (pooled) variance: examples BEQool 2023-04-18 09:59
- Higher-Order Crossovers Helmut 2023-04-20 10:19
- Higher-Order Crossovers BEQool 2023-04-21 07:53

- total (pooled) variance: examples zizou 2023-04-21 21:23
- total (pooled) variance: examples BEQool 2023-04-22 18:20
- total (pooled) variance: examples zizou 2023-04-22 21:06
- total (pooled) variance: examples BEQool 2023-04-25 10:57
- total (pooled) variance: examples zizou 2023-04-25 22:43
- total (pooled) variance: examples BEQool 2023-05-04 08:17

- total (pooled) variance: examples zizou 2023-04-25 22:43

- total (pooled) variance: examples BEQool 2023-04-25 10:57

- total (pooled) variance: examples zizou 2023-04-22 21:06

- total (pooled) variance: examples BEQool 2023-04-22 18:20

- Higher-Order Crossovers Helmut 2023-04-20 10:19

- Parallel designs (total variance) Nav Coelho 2007-07-20 18:38
- Sample size estimation for parallel design Dipesh Jayswal 2007-07-24 08:52

- Parallel designs (total variance)Helmut 2007-07-20 16:29